1. Field of the Invention
The present invention is directed to a generator for generating acoustic traction pulses having a pressure pulse source, a reflector having a negative reflection factor and an acoustic propagation medium filling out at least the space between the pressure pulse source and the reflector.
2. Description of the Prior Art
Medical therapy devices are known which generate a negative pressure pulse, commonly referred to as a rarefaction or tensile pulse, wherein an inversion of the operational sign of the pressure pulse incident into the reflector, and emanating positive from the pressure pulse source, occurs given reflection at a reflector having a negative reflection factor. The term "pressure pulse" shall be employed below exclusively for pressure pulses having a positive operational sign. Generators that are capable of generating rarefaction pulses are employed for treating pathological tissue modifications, for example tumors. There are indications that the cavitation phenomena in the pathological tissue occurring due to irradiation with rarefaction pulses lead to cell damage that at least opposes the further spread of the pathological tissue modifications.
German OS 38 06 532 discloses a generator of this type, however, no details are provided about the structure of the reflector having a negative reflection factor. Such generators have been tested with reflectors formed of a foamed material having closed pores. As a result of the gas enclosed in the pores, such foams are acoustically softer than the standard propagation media, which are usually liquid. As a consequence of the fact that the material of the reflector is acoustically softer than the acoustic propagation medium, i.e. has a characteristic acoustic impedance that is lower than that of the acoustic propagation medium, there is a negative reflection factor between the acoustic propagation medium and the reflector. Pressure pulses incident into the reflector are thus reflected as rarefaction pulses. The tested generators were in fact fundamentally functional; however, there is a risk that the pore walls of the foamed material will become perforated if subjected to the influence of pressure pulses over a longer period of time. This results in the liquid acoustic propagation medium penetrating into the formed material so that the reflector and thus the generator, can no longer function as desired. There is also the risk that liquid acoustic propagation medium will slowly diffuse into the foamed material, likewise leading to a malfunction of the generator.